Re: 6.8 AR ?
I'd stick with what I know works...DPMS (308,223,260,300 SAUM)
That said I don't get the 6.8. I recently sold my nice Model 8 Remington in 25 Remington (a necked down 30 Rem which the 6.8 is based on) and it had as good ballistics to a 6.8. Now for years the "experts" have told us that the 25 Rem & 25-35 were "marginal" deer cartridges so............
A 308 does so much more, so the 6.8 is a "why bother" proposition to be unless you have a ton of AR 15/M16 lowers gathering dust. In a bolt gun it makes no sense as the 260 or 7mm08 will blow it so far away you can't find it.
Seems like all we hear about is small (17 HMR) or big (458 Lott). Reminds me of 1950s Detroit iron "model year changes".
To paraphrase Finn: "If you're hunting in the lower 48 and can't kill it with a 308, you should take up golf."